Research Project V includes two Sub-Projects focused on key new aspects of the genomics, pathogenesis and vaccinology of the two leading Category B low-dose enteropathogens, and on their detection in clinical and environmental samples. These include the highly chlorine-resistant Cryptosporidium parvum, the most fearsome Shigella threat (S. dysenteriae 1) and the largely untreatable, Shiga toxin-producing enterohemorrhagic E. coli. These three pathogens all pose serious risks as low infectious dose agents of bioterrorism as well as major national and global health endemic and epidemic challenges. The team of investigators for this project has a very strong track record of working with these organisms. Led by experienced investigators with international reputations in enteric diseases, Richard L. Guerrant and James B. Kaper, this project builds upon highly productive expertise and upon longstanding and new cross-institutional synergies at UVa, UMd, VCU, VT, USUHS, UVt, and JHU. Our first Sub-Project V.1, on "Cryptosporidium genomics, pathogenesis and vaccinology" builds upon the near complete sequencing of the human (type 1) C. parvum genome by the VCU group, the published tissue culture, animal and field experience with Cryptosporidium by the UVa group, the plant-based production of mucosal vaccines at VT and on studies of the genetics of susceptibility at UVa, UVt, and JHU to identify and express type 1 (human) C. parvum candidate genes, define their roles in pathogenesis and immunity, express promising candidates and define genetic determinants of human susceptibility and thus optimal approaches to vaccine development. Sub-Project V.2 will engage UMd, USUHS and UVa colleagues to construct novel Shigella dysenteriae and enterohemorrhagic E. coli (EHEC) vaccines and develop novel therapeutics for EHEC disease.